Evidence for a role of endogenous estrogen on follicular growth in immature female rats.

Abstract

The effect of gonadotropin and endogenous estrogen on the growing follicles (especially in relation to the presence or absence of theca cell layers) was studied morphometrically in intact immature female rats, using a chemical antiestrogen.When pregnant mare serum gonadotropin (PMSG) was given in combination with clomiphene, the uterine weight decreased significantly as compared with that in the animals treated with PMSG alone (p<0.001). The administration of clomiphene and PMSG did not have a significant effect on the total number of follicles (growing plus atretic). The number of atretic follicles in those treated with PMSG alone tended to decrease as compared with sesame oil-treated animals. However, when PMSG was given in combination with clomiphene, the number of atretic follicles increased significantly as compared with the animals treated with PMSG alone (p<0.05). The number of growing follicles in the animals treated with PMSG alone tended to increase as compared with the animals treated with neither PMSG nor clomiphene. In contrast, when PMSG was given in combination with 5mg/day of clomiphene, the number of growing follicles tended to decrease. The administration of PMSG alone and PMSG combined with 1 and 5mg/day of clomiphene caused a significant decrease in the number of growing follicles without theca cell layers, as compared with sesame oil-treated animals (p<0.05, p<0.01 and p<0.001, respectively). On the other hand, the number of growing follicles with theca cell layers was increased markedly by the administration of PMSG alone (p<0.05).It is suggested that the early stage of follicular growth in the absence of theca cell layers may be promoted by endogenous estrogen. In the presence of theca cell layers, in addition to being mediated by estrogen, gonadotropin-induced follicular growth may be promoted by the maturative effect of gonadotropin itself.